But the LSHTM scientists say the role of the repellent in the deaths was "purely speculative" and they could have been down to other medication the people were taking at the time.

After trawling through the available medical literature, they concluded that the 14 cases of Deet-related encephalopathy recorded since 1957 was "small" compared with 200 million applications of the repellent across the world every year.

'No evidence' for Marmite

The paper looked at other commonly held beliefs about bite prevention and concluded there was "no evidence" that eating Marmite or garlic worked.

Lead researcher Dr James Logan, at the LSHTM, said there were "always a lot of rumours" around Deet, and that it was often "mixed up" with the pesticide DDT, which was used to kill insects.